Energy storage system and method for controlling the same

1. An energy storage system configured to be coupled to at least one of a power generation system which is a system for generating power using an energy source, a grid comprising a power generating station, or a load, the energy storage system comprising: a battery system comprising at least one rack, the at least one rack comprising a rack controller configured to obtain a temperature of at least one battery; and a system controller configured to control a charging operation and a discharging operation of the at least one battery on the at least one rack in accordance with the obtained temperature of the at least one battery received from the rack controller, the system controller comprising a battery temperature determination unit and a current controller, the battery temperature determination unit being configured to compare the obtained temperature with a reference temperature, and the current controller being configured to: control a first current discharging operation of the at least one battery at a first current when the obtained temperature is greater than or equal to the reference temperature; and control a second current discharging operation at a second current when the obtained temperature is less than the reference temperature, wherein the first current is greater than the second current, wherein the rack further comprises at least one battery tray on which the at least one battery is located, the at least one battery tray comprising a tray controller, and wherein the rack controller is configured to receive the obtained temperature of the at least one battery from the tray controller of the at least one battery tray corresponding to the at least one battery.

2. The energy storage system of claim 1 , wherein the rack controller is configured to obtain the temperature of the at least one battery when the charging operation or the discharging operation is performed.

3. The energy storage system of claim 1 , wherein the rack controller is configured to transmit the obtained temperature to the system controller periodically.

4. The energy storage system of claim 1 , wherein the rack controller is configured to transmit the obtained temperature to the system controller in response to a command from the system controller to transmit the obtained temperature.

5. The energy storage system of claim 1 , wherein the rack controller is further configured to determine whether or not more than a reference time has elapsed since the obtaining of the temperature, and to obtain the temperature again and transmit the obtained temperature to the system controller when more than the reference time has elapsed.

6. The energy storage system of claim 1 , wherein the reference temperature is selectable.

7. The energy storage system of claim 1 , wherein the system controller is configured to change the first current to the second current when the obtained temperature becomes greater than or equal to the reference temperature.

8. The energy storage system of claim 1 , wherein the system controller is configured to determine receipt of the obtained temperature from the rack controller.

9. The energy storage system of claim 1 , further comprising a converter configured to change a current, wherein the current controller is configured to control the converter to determine current level between the first current and the second current.

10. The energy storage system of claim 1 , wherein the rack controller comprises a temperature measuring unit configured to obtain the temperature of the at least one battery.

11. The energy storage system of claim 1 , further comprising a rack bus, wherein the rack controller and the tray controller of the at least one battery tray are configured to communicate with each other via the rack bus.

12. The energy storage system of claim 1 , wherein the battery system further comprises a rack protection circuit configured to block power supply under control of the rack controller.

13. The energy storage system of claim 12 , wherein the rack protection circuit is further configured to obtain a voltage and a current of the battery system, and to transmit the obtained voltage and the obtained current to the system controller.

14. A method of controlling discharging of a battery in an energy storage system comprising: a system controller; and a rack comprising a rack controller, the rack comprising a battery tray on which the battery is arranged and which comprises a tray controller, the energy storage system being configured to be coupled to at least one of a power generator for generating power using an energy source, a grid comprising a power generating station, or a load, the method comprising: obtaining a temperature of the battery arranged on the battery tray; transmitting the obtained temperature from the tray controller to the rack controller and then from the rack controller to the system controller; comparing the obtained temperature of the battery with a reference temperature; and controlling a discharging operation of the battery in accordance with the obtained temperature, wherein the battery undergoes a second-current discharging operation when the obtained temperature is less than the reference temperature, and undergoes a first-current discharging operation when the obtained temperature is greater than or equal to the reference temperature, and wherein a second current corresponding to the second-current discharging operation is less than a first current corresponding to the first-current discharging operation.